The present invention relates generally to rotating machinery, and more particularly to a method and apparatus for cooling a rotating machine such as an air-cooled motor utilizing a plurality of shaft-mounted fan assemblies adapted to cool the motor interior and exterior case by moving air.
Conventional electric motors have a stator section and a rotor section, the latter typically mounted to a central shaft. Although the windings which form the stator section are typically manufactured of a low-resistance material, such as copper wire, the passage of electrical current through the motor windings generates heat. Excessive heat is harmful to non-metallic components of the motor (e.g., electrical insulation, seals and gaskets) and potentially reduces motor life. Moreover, heat will cause metal components to expand, resulting in increased friction and wear and also resulting in reduced motor efficiency and power output. Thus, it is common to equip air-cooled motors with a fan to help dissipate heat to avoid so-called I2R efficiency losses.
Various single and dual fan arrangements are known in the art for cooling rotary machine components, including electric motor parts. Some arrangements, more preferable air-cooled machines, attempt to exchange the air within the motor case to dissipate heat by convection. Air is circulated over the machine components, draws heat from the components, and delivers the heat to the atmosphere surrounding the machine when exhausted from the machine.
For example, U.S. Pat. No. 4,742,257 discloses a totally enclosed fan cooled induction motor which has a pair of internal fans disposed on opposite ends of the shaft that move air internal to the case. The motor also has an external fan that moves air externally over the internal and external case. The two fans do not cooperate with one another in any manner and do not share air between them.
Geberth Jr., U.S. Pat. No. 4,908,538 discloses a totally enclosed electric motor that utilizes an external fan to move air over an exterior surface of a motor case and an internal fan to move air within the interior of the motor case. Air between the interior and exterior of the motor case does not mix and the two fans do not cooperate with one another in any manner. The interior air flow transfers heat from the machine or motor component to the moving air within the interior and by convection to the exterior case. The air in the interior of the motor is not exchanged.
Bagherpour et al. U.S. Pat. No. 5,751,079 discloses an alternator motor with both internal and external fans. Each of the fans cools separate portions of the motor with no cooperation between the internal and external fans.
Lukens U.S. Pat. 3,643,119 discloses a ventilated dynamo electric machine utilizing two fans to cool components of the machine. A first fan draws air into one end where the air is divided into a plurality of flow paths within the machine case. A separate fan at the opposite end pulls air through the case. Each of the fans is arranged to move air in the same direction and neither of the fans moves air over the exterior of the motor case.
There is a need for an enhanced cooling apparatus and method for rotating machinery such as air-cooled electric motors.
Objects, features and advantages of the present invention are inherent in the rotary machine and method disclosed in the written description and accompanying drawings provided herein. In one example of the invention, a rotary machine has a case with an exterior surface, a drive end, an opposite end, and an interior working chamber. A rotary shaft is supported for rotation within the case interior chamber between the drive end and the opposite end. At least one machine component is supported on the rotary shaft and rotates along with the shaft. At least one air inlet and at least one air outlet are provided in the case and communicate with the working chamber. A first fan assembly is supported for rotation on the rotary shaft within the case interior and is arranged for moving air through the air inlet into the interior, for moving the air over the at least one machine component, and for moving air out the air outlet from the working chamber. A cowl is mounted adjacent the opposite end of the case and defines a plenum between an interior surface of the cowl and an end surface of the case opposite end. The cowl defines an annular air exhaust opening around a cowl perimeter adjacent the case exterior surface. A second fan assembly is disposed within the plenum whereby the second fan and plenum are arranged for assisting the first fan assembly in moving air out the air outlet and further for moving air toward the end surface of the case opposite end such that the air exits the plenum throughout the annular exhaust opening and passes back over the exterior surface of the case.
In one example of the invention, a method of cooling a rotary machine is provided wherein the machine has a case, a rotary shaft supported within an interior working chamber of the case, and at least one machine component supported for rotation on the rotary shaft in the case interior working chamber. The method includes providing at least one air inlet and providing at least one air outlet each in communication with the working chamber. A first fan assembly is positioned within the interior working chamber and mounted for rotation on the rotary shaft. A second fan assembly is positioned within a plenum mounted exterior to the case adjacent one end of the machine and is mounted for rotation with the rotary shaft. The first fan assembly is arranged for moving air into the case interior via the air inlet, for moving air over the at least one machine component, and for moving air out of the case via the air outlet. The second fan is arranged for moving air back toward an end surface of the case and back over an exterior surface of the case and is also arranged for assisting the first fan assembly in moving air from the case interior via the air outlet. The motor is operated to rotate the rotary shaft which in turn rotates the fans to air-cool the motor during operation by moving air through the working chamber over the at least one machine component and simultaneously moving air over the exterior surface.